German patent specification No. 20 24 210 discloses a method of producing active coke by thermal treatment of coal, wherein raw brown coal or lignite is treated after drying in a vacuum shaft coker, the treatment being effected, in at least one of the method steps, at a reduced pressure of less than 1 Torr. This method indeed produces a usable active coke, but it cannot generally be carried out with sufficient cost-effectiveness that the active coke which is produced thereby can be economically used for all uses which are technically possible. Furthermore, this method is not suitable for re-activating coke whose adsorption capacity has been partly or totally exhausted by virtue of the coke having adsorbed substances to be so treated, such coke being referred to herein as charged coke, and in practice, the method must be specifically adapted to the production of active coke, in respect of all its method steps.